Moisture barrier film

ABSTRACT

A multiple layer film useful in moisture barrier packaging applications has at least one layer comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; and two additional layers comprising a propylene polymer or copolymer, ethylene alpha olefin copolymer, ionomer, polybutene, or blends thereof. A core layer of ethylene vinyl alcohol copolymer or other oxygen barrier material, or high density polyethylene, can be included in some embodiments. A preferred embodiment of the multi-layer film exhibits excellent moisture barrier and optical properties, and shrink properties as well if the film has been oriented. High oxygen barrier is also a feature in embodiments including EVOH or other oxygen barrier materials.

This is a Divisional Application of application Ser. No. 08/358,121, filed Dec. 16, 1994 , now U.S. Pat. No. 5,543,223, which is Divisional Application of application Ser. No. 08/116,798 filed Sep. 10, 1993, now U.S. Pat. No. 5,482,771, which is a Continuation-In-Part of application Ser. No. 07/947,244 filed Sep. 18, 1992, now abandoned.

FIELD OF THE INVENTION

This invention relates to thermoplastic films for packaging; and more particularly, this invention relates to a multi-layer film having high moisture barrier characteristics.

BACKGROUND OF THE INVENTION

Thermoplastic film, and in particular polyolefin materials, have been used for some time in connection with packaging of various articles including food products which require protection from the environment, an attractive appearance, and resistance to abuse during the storage and distribution cycle. Suitable optical properties are also desirable in order to provide for inspection of the packaged product after packaging, in the distribution chain, and ultimately at point of sale. Optical properties such as high gloss, high clarity, and low haze characteristics contribute to an aesthetically attractive packaging material and packaged product to enhance the consumer appeal of the product.

Various polymeric materials have been used to provide lower moisture permeability in order to reduce the transmission of moisture through the packaging film and thereby extend the shelf life of products such as food, medical, electronic, and other items which are sensitive to moisture gain or loss. For some products, maintenance of a high moisture content is desirable, and the film ideally minimizes loss of moisture from the package to the environment. For other products, maintenance of a low moisture content is desirable, and the film ideally minimizes gain of moisture from the environment through the packaging material.

It is also often desirable to include in a packaging film a shrink feature, i.e., the propensity of the film upon exposure to heat to shrink or, if restrained, create shrink tension within the packaging film. This property is imparted to the film by orientation of the film during its manufacture. Typically, the manufactured film is heated to its orientation temperature and stretched in either a longitudinal (machine) or transverse direction (i.e. monoaxial orientation), or both directions (i.e. biaxial orientation), in varying degrees to impart a certain degree of shrinkability in the film upon subsequent heating. When biaxial orientation is done, it can be simultaneous or sequential; that is, the orientation can be done in each of the directions in turn, or else both the longitudinal and transverse orientation can be done at the same time. Any suitable technique, such as blown bubble or tenterframing, can be used to achieve orientation of the film. After being so stretched, the film is rapidly cooled to provide this latent shrinkability to the resulting film. One advantage of shrinkable film is the tight, smooth appearance of the wrapped product that results, providing an aesthetic package as well as protecting the packaged product from environmental abuse. Various food and non-food items may be and have been packaged in shrinkable films.

It is sometimes also desirable to orient a packaging film and thereafter heat set the film by bringing the film to a temperature near its orientation temperature. This produces a film with substantially less shrinkability, while retaining much of the advantages of orientation, including improved tensile strength, modulus and optical properties.

It is an object of the present invention to provide a thermoplastic multilayer film characterized by good moisture barrier properties.

It is a further object of the present invention to provide a thermoplastic multilayer film having an aesthetic appearance with good clarity, and other desirable optical properties.

It is another object of the present invention to provide a thin thermoplastic multilayer film having toughness and abrasion resistance.

It is still another object of the present invention to provide a thermoplastic multilayer film which may be totally coextruded, oriented, and have good moisture barrier and, in some cases, both moisture barrier and oxygen barrier properties.

Of interest are U.S. Pat. Nos. 4,921,749 (Bossaert et al); 5,085,943 (Crighton et al); 5,091,237 (Schloegel et al); 5,128,183 (Buzio); and 5,212,009 (Peiffer et al) disclosing the use of hydrocarbon resins.

SUMMARY OF THE INVENTION

The present invention relates to a thermoplastic multi-layer film comprising a core layer comprising a blend of propylene polymer or copolymer, or ethylene alpha olefin copolymer, and a hydrocarbon resin; and two outer layers comprising a propylene polymer or copolymer, ethylene alpha olefin copolymer, polybutene, or blends thereof. In another aspect, the present invention relates to a thermoplastic multi-layer film comprising a core layer comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; two intermediate layers, on opposite surfaces of the core layer, comprising propylene polymer or copolymer, or a polymeric adhesive; and two outer layers comprising a propylene polymer or copolymer, ethylene alpha olefin copolymer, ionomer, polybutene, or blends thereon.

The present invention also relates to a thermoplastic multi-layer film comprising a core layer comprising an ethylene alpha olefin copolymer, ethylene propylene copolymer, rubber modified ethylene propylene copolymer, or ethyene propylene butene terpolymer; two intermediate layers, on opposite surfaces of the core layer, comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; and two outer layers comprising a propylene polymer or copolymer, ethylene alpha olefin copolymer, ionomer, polybutene, or blends thereof.

A film with oxygen barrier as well as moisture barrier properties comprises a core layer comprising an oxygen barrier material; two intermediate layers, on opposite surfaces of the core layer, comprising a polymeric adhesive; two outer layers comprising a blend of propylene polymer or copolymer, or polybutene, and a hydrocarbon resin; and a polymeric sealant layer adhered to at least one of the outer layers.

An alternative film with at least seven layers comprises a core layer comprising high density polyethylene; two intermediate layers, on opposite surfaces of the core layer, comprising a polymeric adhesive, ethylene vinyl acetate copolymer, or ethylene alpha olefin copolymer; two outer layers comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; and two outermost layers comprising propylene polymer or copolymer, polybutene, or blends thereof.

Another alternative is a film comprising a core layer comprising an oxygen barrier material; two intermediate layers, on opposite surfaces of the core layer, comprising polyamide; two tie layers, each disposed on a respective polyamide layer, comprising a polymeric adhesive, ethylene alpha olefin copolymer, or ethylene vinyl acetate copolymer; two moisture barrier layers, adhered to respective adhesive layers, comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; and two outermost layers comprising a propylene polymer, propylene copolymer, ethylene alpha olefin copolymer, or polybutene.

In another aspect of the invention, a method of making a thermoplastic multilayer film comprises the steps of coextruding an interior layer of a blend of propylene polymer or copolymer, and a hydrocarbon resin, and two outer layers comprising a propylene polymer or copolymer, ethylene alpha olefin copolymer, polybutene, or blends thereof; cooling the coextruded multilayer film; and collapsing the cooled film.

DEFINITIONS

"Hydrocarbon resin" ("HC" herein) and the like as used herein means resins made by the polymerization of monomers composed of carbon and hydrogen only. Thermoplastic resins of low molecular weight made from relatively impure monomers derived from coal-tar fractions, petroleum distillates, etc. are also included. A discussion of HC resins can be found e.g. in U.S. Pat. Nos. 4,921,749 (Bossaert et al); 5,091,237 (Schloegel et al); and 5,128,183 (Buzio).

"Ethylene alpha olefin copolymer" (EAO) is used here to include such materials as linear low density polyethylene (LLDPE); very low and ultra low density polyethylene (VLDPE and ULDPE); and metallocene catalyzed polymers such as those supplied by Exxon. Tafmer (tm) materials supplied by Mitsui are also included. These materials generally include copolymers of ethylene with one or more comonomers selected from C₄ to C₁₀ alphaolefins such as butene-1, hexene-1, octene-1, etc. in which the molecules of the copolymers comprise long chains with relatively few side chain branches or cross-linked structures. This molecular structure is to be contrasted with conventional low or medium density polyethylenes which are more highly branched than their respective counterparts. "LLDPE" as defined here has a density in the range of from about 0.916 grams per cubic centimeter to about 0.940 grams per cubic centimeter. Generally, "EAO" as used here includes both homogeneous and heterogeneous polymers.

"Intermediate layer" and the like is used herein to define a layer in a multi-layer film enclosed on both sides by other layers, i.e. disposed between other layers of the film.

The term "oriented" and the like is used herein to define a polymeric material in which the molecules have been aligned in the longitudinal and/or transverse direction by a process such as a tenter frame or blown bubble process.

"Propylene polymer" and the like is used here to mean polymerized propylene in its homopolymer form, and "propylene copolymers" means copolymers such as ethyene propylene copolymer, where generally small amounts of a comonomer such as ethylene are included in the copolymer. Terpolymers are also included.

"Polymeric adhesive" and the like here means polymeric materials, of any suitable composition, which can be used to create or enhance interlaminar bonds in multilayer thermoplastic films. Polyolefins are preferred, especially those which have been modified, e.g. by carboxylic acid or acid anhydride in a graft copolymer.

"Rubber modified EPC" and the like here means an EPC which has been modified by the inclusion of other moieties in the polymer structure. Such material may provide improved elasticity or other properties. An example is believed to be Himont KS-052 P, or those available from Rexene (El Paso).

"Ethylene propylene butene terpolymer" and the like is used here to mean a terpolymer incorporating these three comonomers in various percentages. An example is KT-021 from Himont, or those available from Sumitomo.

"Core layer" as used herein means an intermediate layer of a multilayer film, and the central layer where the film has an odd number of layers.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details are given below with reference to the drawing figures wherein :

FIG. 1 is a schematic cross section of a preferred embodiment of a multi-layer moisture barrier film of the invention, and

FIGS. 2 and 3 are alternative embodiments of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring specifically to the drawings, in FIG. 1, a schematic cross section of a preferred embodiment of the multi-layer moisture barrier film of the invention is shown. The multi-layer film 10 has the generalized structure of A/B/A where A is an outer layer, and B is a core layer comprising a moisture barrier material.

Core layer 12 preferably comprises a blend of a propylene polymer or copolymer, and a hydrocarbon resin, this blend shown as a spotted/striped layer. A typical example of a propylene homopolymer is Exxon PD 4062 E7, or those available from Fina, or Himont PD 064. A preferred propylene copolymer is ethylene propylene copolymer sold under the designation Fina 8473 or Fina 8473X. This material has an ethylene content of about 4%. A preferred hydrocarbon resin is Regalrez 1128 or 1139 from Hercules. The HC resin preferably comprises between about 30% and 50% by weight of the blend.

Outer layers 14 and 16 are preferably ethylene propylene copolymer (EPC), polypropylene (PP), or blends thereof. If only polypropylene resin is used, the film can be difficult to use for packaging applications involving heat sealing. Therefore, it is preferable to use EPC alone, or the blend of the two materials. Commercial resin examples are those discussed above for core layer 12. An alternative polypropylene for the outer layers 14 and 16 is Himont PDO 64. These blend layers may include from 0-100% EPC and 100%-0% PP, although preferably the blend layers include between about 96% and 85% EPC and between about 4% and 15% PP; even more preferably, the blend layer includes about 92% EPC and 8% PP. EAO and polybutene can also be used in the outer layers.

In FIG. 2, a schematic cross section of another embodiment of the multi-layer moisture barrier film of the invention is Generally shown. The multi-layer film has the structure of A/B/C/B/A where A is an outer layer, B is an intermediate adhesive layer, and C is a core layer comprising a moisture barrier material.

The core layer preferably comprises a blend of a propylene polymer or copolymer, and a hydrocarbon resin. Suitable materials are those described above for core layer 12 of film 10.

The outer layers are preferably the materials discussed above for outer layers 14 and 16 of film 10. The outer layers also preferably include an HC such as described for core layer 12 of film 10.

The intermediate layers preferably comprise a propylene polymer or copolymer, or blends thereof, optionally blended with hydrocarbon resin.

An alternative A/B/C/B/A structure is also within the scope of this invention, and specifically shown by the position of the moisture barrier layers in the film of FIG. 2.

In this alternative, core layer 24 preferably comprises an ethylene alpha olefin copolymer, more preferably a linear EAO. Very low density polyethylene (VLDPE), and linear low density polyethyene (LLDPE) are preferred. A suitable LLDPE is Dowlex 2045. The core layer 24 can also comprise EPC, a rubber modified EPC, or an ethylene terpolymer, especially an ethylene propylene butene terpolymer such as KT 021 P from Himont.

Outer layers 20 and 28 are preferably the materials discussed above for outer layers 14 and 16 of film 10.

Intermediate layers 22 and 26 preferably comprise a blend of a propylene polymer or copolymer, and a hydrocarbon resin. Suitable materials are those described above for core layer 12 of film 10. An alternative material for layers 22 and 26 is Exxon 6042, which is believed to be a blend of polypropylene and hydrocarbon resin.

In FIG. 3, a schematic cross section of another embodiment of the multi-layer moisture barrier film of the invention is shown. The multi-layer film 30 has the generalized structure of A/B/C/D/C/B/A where A is an outer layer, B is a moisture barrier layer, C is an intermediate adhesive layer, and D is a core layer comprising an oxygen barrier material.

Core layer 38 preferably comprises an oxygen barrier material such as ethylene vinyl alcohol copolymer, vinylidene chloride copolymer, polyester, or polyamide.

Outer layers 32 and 44 are preferably the materials discussed above for outer layers 14 and 16 of film 10.

Intermediate layers 36 and 40 preferably comprise a propylene polymer or copolymer, such as Exxon PD 4062 E7. Alternative materials are polymeric adhesives, especially carboxylic acid or maleic anhydride-modified polyolefins and more preferably polypropylene-based carboxylic acid or maleic anhydride-modified adhesives. Conventional lamination or other suitable methods may sometimes be necessary, depending on the nature of the respective layers, to ensure adequate interlaminar bond strength.

Moisture barrier layers 34 and 42 preferably comprise a blend of a propylene polymer or copolymer, and a hydrocarbon resin. Suitable materials are those described above for core layer 12 of film 10. An alternative material for layers 34 and 42 is Exxon 6042.

An alternative film with at least seven layers comprises a core layer 38 comprising high density polyethylene; two intermediate layers 36 and 40, on opposite respective surfaces of the core layer, comprising a polymeric adhesive, ethylene vinyl acetate copolymer, or ethylene alpha olefin copolymer; two moisture barrier layers 34 and 42 comprising a blend of propylene polymer or copolymer and a hydrocarbon resin; and two outermost layers 32 and 44 comprising propylene polymer or copolymer.

A multilayer film of four or six layers, and/or possessing both moisture barrier and oxygen barrier properties, can also be made in accordance with the present invention. In such alternative constructions, a blend of HC resin with propylene polymer or copolymer can be present in any of the layers of the multilayer film.

The core, intermediate, and moisture barrier layers of such a film can be like that of film 30. A sealant layer is coextruded with, or extrusion coated, extrusion laminated, or adhesive laminated, by means and methods well known in the art, to one of the moisture barrier layers. The sealant layer, which can be disposed on one or both outer surfaces of the film structure, preferably comprises an ethylene alpha olefin copolymer, more preferably a linear EAO. Very low density polyethylene (VLDPE), and linear low density polyethyene (LLDPE) are preferred. A suitable LLDPE is Dowlex 2045. The sealant layer can also comprise EPC, a rubber modified EPC, an ethylene propylene butene terpolymer such as KT 021 P from Himont, an ethylene vinyl acetate copolymer, an ethylene alkyl acrylate copolymer, an ethylene acrylic or methacrylic acid copolymer, or an ionomer.

The films of the present invention can be made by coextrusion, extrusion coating, extrusion laminating, and conventional adhesive lamination techniques well known in the art, using annular or slot die extrusion equipment as appropriate.

The beneficial low moisture transmission rates (high moisture barrier) and other properties associated with exemplary films of the present invention are demonstrated in the Tables.

The resins used in these examples are identified in Table 1, and the films made from these resins are identified in Tables 2 through 8.

Physical properties of these films are itemized the remaining Tables. Values given are typically average values obtained from four replicate measurements; values for MVTR are average obtained from three samples.

The terms and abbreviations In the Tables have the following meaning:

"PP"=polypropylene.

"EPC"=ethylene propylene copolymer.

"EAO"=ethylene alpha olefin copolymer.

"EPB"=ethylene propylene butene terpolymer.

"EVOH"=ethylene vinyl alcohol copolymer.

"ADH"=polymeric adhesive; ADH 1 is an ethylene butene-based adhesive from Du Pont; ADH 2 is an EPC-based adhesive from Mitsui.

"AB"=antiblock.

"MO"=mineral oil.

"Tensile"=tensile at break and 73° F., in PSI (ASTM D 882-81).

"PSI"=pounds per square inch (ASTM 882-81).

"Unshrunk"=a film sample or samples that were not shrunk by exposure to heat at the time of testing for the stated property.

"Shrunk"=a film sample or samples that were shrunk by exposure to heat at the time of testing for the stated property.

"LD"=longitudinal orientation direction.

"TD"=transverse orientation direction.

"Modulus"=modulus of elasticity (ASTM 882-81) in PSI at 73° F.

"Haze"=haze (ASTM D 1003-61 (reapproved 1977)) in per cent.

"Clarity"=total light transmission (ASTM D 1003 Method A) in percent.

"Gloss"=gloss measured at 45° angle to film surface (ASTM D 2457-70 (reapproved 1977)).

"MVTR 1"=moisture (water) vapor transmission rate (ASTM F 372) in grams/24 hours, 100 square inches at 100% relative humidity and 100° F.

"MVTR 2"=moisture (water) vapor transmission rate (ASTM F 372) in grams/24 hours, 100 square inches at 90% relative humidity and 100° F.

"OTR"=oxygen transmission rate (ASTM D 3985-81) in cc at standard temperature and pressure, in 24 hours, per square meter, at one atmosphere, at 0% relative humidity.

"Tear"=tear propagation in grams at 73° F. (ASTM D 1938-79).

"Film Thickness"=the average thickness (gauge) of the film samples in mils (=0.001 inches).

"Tensile"=tensile strength at break (ASTM D 882-81) in psi.

"Elongation"=elongation at break (ASTM D 882-81) in percent.

"Ball Burst"=ball burst impact in centimeters-kilograms at 73° F. (ASTM D 3420-80).

                  TABLE 1     ______________________________________     MATERIAL     TRADENAME      SUPPLIER     ______________________________________     PP 1         Profax PD-064  Himont     PP 2*         see footnote!     PP 3         PD 4062        Exxon     PP 4**       Escorene PD 6042                                 Exxon                   see footnote!     EPC 1        Fina 8473 or   Fina                  Fina 8473 X     EPC 2***      see footnote!     EPC 3        PD 9302        Exxon     EPB 1        KT-021         Himont     HC 1         Regalrez 1128  Hercules     HC 2         Escorez 5340   Exxon     HC 3         Regalrez 1139  Hercules     EAO 1        Dowlex 2045.03 Dow     EAO 2        Dowlex 2045.04 Dow     ADH 1        Bynel CXA 4104 Du Pont     ADH 2        Admer QF 551 A Mitsui     EVOH 1       EVAL SC H-103  Evalca     EVOH 2       EVAL LC F-101 A                                 Evalca     EVOH 3       EVAL LC H-103  Evalca     MO 1         Kaydol         Witco     ______________________________________      **PP 2 is a masterbatch blend of PP 1 with about 4%, by weight of the      blend, of a silicacontaining antiblocking agent, about 5% by weight of      amide waxes, and about 1% of a lubricating agent. The amide waxes and      lubricating agent are well known in the art as slip agents.      **PP 4 is Escorene PD 6042, believed to be a blend of polypropylene and      hydrocarbon resin.      ***EPC 2 is a blend of EPC 1 blended with about 1.5%, by weight of the      blend, of an antiblock agent, and 0.5%, by weight of the blend, of a      mineral oil.

TABLE 2(CONTROL)

Initial efforts to make a moisture barrier material involved the use of homopolymer polypropylene in a core layer, with sealant layers of propylene copolymer on both surfaces of the core layer. The object was to maximize thickness of the core layer to minimize the moisture vapor transmission rate (MVTR), while still maintaining adequate free shrink and sealability properties of the film. The MVTR did not prove adequate for at least some moisture barrier packaging applications. An example of this film is given below:

EXAMPLE Film Structure

1. 92% EPC 1+8% PP 2/PP 1/92% EPC 1+8% PP 2

The generalized structure of the film of Example 3 was A/B/A.

Relative layer thickness ratios: A=1.0; B=2.0; A=1.0.

TABLE 3

The films of Table 3 were made in an effort to make a moisture barrier material with lower MVTR. This was achieved using hydrocarbon resin blended with homopolymer polypropylene. It was found that these formulations had much lower moisture vapor transmission rate (MVTR) than those of Table 2. However, they could not be oriented much over 4.5×4.5 racking (orientation) ratio because of equipment limitations. On other equipment, e.g. a modified bubble process or tenterframing, higher orientation (racking) rates can be achieved. They also could not be made into heavier gauge films because of relatively poor tear properties. Examples of these films are given below:

EXAMPLE Film Structure

2. 90% 92% EPC 1+8% PP 2!+10% HC 1 PP 3

84.5% PP 3+15% HC 1+0.5% MO 1 PP 3

90% 92% EPC 1+8% PP 2!+10% HC 1

The generalized structure of the film of Example 2 was A/B/C/B/A.

Relative layer thickness ratios: 2.5:0.8:3.7:0.6:2.4.

3. 92% EPC 1+8% PP 2/PP 4/92% EPC 1+8% PP 2

The generalized structure of the film of Example 3 was A/B/A.

Relative layer thickness ratios: 1:2:1.

4. 92% EPC 1+8% PP 2/PP 4/92% EPC 1+8% PP 2

The generalized structure of the film of Example 4 was A/B/A.

Relative layer thickness ratios: 1:3:1.

TABLE 4

Alternative films of Table 4 were made in which, in effect, the core layer of the films of Table 3 (i.e. the layer containing the hydrocarbon resin) were "split" into two substrate (intermediate) layers. A "new" core layer of e.g. LLDPE or EPC is introduced. The practical effect of this is to improve tear properties of the film, related to tape creasing during the orientation process, so that it can be oriented at e.g. 6×6 ratio. The film was in fact oriented at 4×4.5 because of the equipment limitations discussed for the Examples of Table 3. Examples of these films are given below:

EXAMPLE Film Structure

5. 92% EPC 1+8% PP 2/PP 4/EAO 1/PP 4/92% EPC 1+8% PP 2

The generalized structure of the film of Example 5 was A/B/C/B/A.

Relative layer thickness ratios: 1.5:3:1:3:1.5.

6. 92% EPC 1+8% PP 2/PP 4/EPC 1/PP 4/92% EPC 1+8% PP 2

The generalized structure of the film of Example 6 was A/B/C/B/A.

Relative layer thickness ratios: 1.5:3:1:3:1.5.

TABLE 5

The inventor took the basic constructions of Table 4, and oriented them at generally higher racking ratios of 6×6. The result was a film showing improvements in (i.e. lower) MVTR. Examples of these films are given below:

EXAMPLE Film Structure

7. 92% EPC 1+8% PP 2/PP 4/EAO 1/PP 4/92% EPC 1+8% PP 2

The generalized structure of the film of Example 7 was A/B/C/B/A. This film was like that of Example 5, but with both MD and TD racking ratios of about 6×6 in the longitudinal and transverse directions respectively.

Relative layer thickness ratios: 1.5:3:1:3:1.5.

8. 92% EPC 1+8% PP 2/PP 4/EAO 1/PP 4/92% EPC 1+8% PP 2

The generalized structure of the film of Example 8 was A/B/C/B/A. This film was like that of Example 7, but oriented at a higher temperature compared to Example 7.

Relative layer thickness ratios: 1.5:3:1:3:1.5.

9. 92% EPC 1+8% PP 2/PP 4/EAO 2/PP 4/92% EPC 1+8% PP 2

The generalized structure of the film of Example 9 was A/B/C/B/A.

Relative layer thickness ratios: 1.5:3:1:3:1.5.

10. 92% EPC 1+8% PP 2/PP 4/EPB 1/PP 4/92% EPC 1+8% PP 2

The generalized structure of the film of Example 10 was A/B/C/B/A.

Relative layer thickness ratios: 1.5:3:1:3:1.5.

11. 92% EPC 1+8% PP 2

70% PP 3+30% HC 2 EAO 2

70% PP 3+30% HC 2

92% EPC 1+8% PP 2

The generalized structure of the film of Example 11 was A/B/C/B/A.

Relative layer thickness ratios: 1.5:3:1:3:1.5.

12. 90% EPC 1+10% PP 2/PP 4/EPC 1/PP 4/90% EPC 1+10% PP 2

The generalized structure of the film of Example 12 was A/B/C/B/A.

Relative layer thickness ratios: 1.5:3:1:3:1.5.

13. 90% EPC 1+10% PP 2/PP 4/EPC 1/PP 4/90% EPC 1+10% PP 2

The generalized structure of the film of Example 13 was A/B/C/B/A. This film was like that of Example 12, but lower racking ratios of 4.5×4.5 to produce a film of 132 gauge thickness.

Relative layer thickness ratios: 1.5:3:1:3:1.5.

14. 90% EPC 1+10% PP 2/PP 4/EPC 1/PP 4/90% EPC 1+10% PP 2

The generalized structure of the film of Example 14 was A/B/C/B/A. This film was like that of Example 13, but with slightly higher racking ratios (4.5×5.0) and a final film thickness of 155 gauge.

Relative layer thickness ratios: 1.5:3:1:3:1.5.

15. 87.5% EPC 3+12.5% PP 2

PP 4

EPC 3

PP 4

87.5% EPC 3+12.5% PP 2

The generalized structure of the film of Example 15 was A/B/C/B/A.

Relative layer thickness ratios: 1.5:3:1:3:1.5.

16. 84% EPC 3+16% PP 2

PP 4

EPC 3

PP 4

84% EPC 3+16% PP 2

The generalized structure of the film of Example 16 was A/B/C/B/A.

Relative layer thickness ratios: 1.5:3:1:3:1.5.

17. 86% EPC 3+14% PP 2

PP 4

EPC 3

PP 4

86% EPC 3+14% PP 2

The generalized structure of the film of Example 17 was A/B/C/B/A.

Relative layer thickness ratios: 1.5:3:1:3:1.5.

TABLE 6

The inventor made a seven layer film (Example 18) as a control, and then made two moisture/oxygen barrier seven-layer films (Examples 19 and 20) with good results. Examples of these films are given below:

EXAMPLE Film Structure

18. 92% EPC 1+8% PP 2

PP 3

ADH 2

EVOH 1

ADH 2

PP 3

92% EPC 1+8% PP 2

The generalized structure of the film of Example 18 was A/B/C/D/C/B/A.

Relative layer thickness ratios: 1:2.5:1:1:1:2.5:1.

19. 92% EPC 1+8% PP 2

PP 4

ADH 1

EVOH 2

ADH 1

PP 4

92% EPC 1+8% PP 2

The generalized structure of the film of Example 19 was A/B/C/D/C/B/A.

Relative layer thickness ratios: 1.5:2:1:1:1:2:1.5.

20. 92% EPC 1+8% PP 2

PP 4

ADH 2

EVOH 3

ADH 2

PP 4

92% EPC 1+8% PP 2

The generalized structure of the film of Example 20 was A/B/C/D/C/B/A.

Relative layer thickness ratios: 1.5:2:1:1:1:2:1.5.

TABLE 7

Two alternative films of seven layers have the structure:

21. 92% EPC 1+8% PP 2

PP 4

EVA 1

HDPE 1

EVA 1

PP 4

92% EPC 1+8% PP 2

The generalized structure of the film of Example 21 is A/B/C/D/C/B/A.

Relative layer thickness ratios: 1:2.5:1:1:1:2.5:1.

22. 92% EPC 1+8% PP 2

PP 4

VLDPE 1

HDPE 1

VLDPE 1

PP 4

92% EPC 1+8% PP 2

The generalized structure of the film of Example 22 is A/B/C/D/C/B/A.

Relative layer thickness ratios: 1:2.5:1:1:2.5:1.

TABLE 8

Two additional alternative films of five layers were made, and are compared in Table 13 with the film of Example 17. These two additional films have the following structures:

23. 86% EPC 3+14% PP 2

PP 4

85% EPC 3+15% HC 3

PP 4

86% EPC 3+14% PP 2

The generalized structure of the film of Example 23 is A/B/C/B/A.

Relative layer thickness ratios: 1.5:3:1:3:1.5.

24. 86% 85% EPC 3+15% HC 31!+14% PP 2

PP 4

85% EPC 3+15% HC 3

PP 4

85% EPC 3+15% HC 3

The generalized structure of the film of Example 24 is A/B/C/B/C.

Relative layer thickness ratios: 1.5:3:1:3:1.5.

                  TABLE 9     ______________________________________            Example 1            (control)                   Example 2  Example 3                                       Example 4     ______________________________________     Modulus     LD       239,480  279,920    316,030                                         336,820     TD       214,690  260,240    298,930                                         316,820     Free Shrink/Shrink Tension     at 200° F.:     LD        7/396    9/321     10/315 11/408     TD       12/388   14/381     17/528 17/504     at 220° F.:     LD       12/435   14/335     14/361 15/439     TD       18/432   19/383     24/540 25/548     at 240° F.:     LD       18/451   20/364     20/443 22/494     TD       26/469   28/413     33/591 33/516     at 260° F.:     LD       31/473   31/397     33/429 33/511     TD       35/493   39/441     45/538 44/561     Haze     Unshrunk 1.2      1.7        1.3    1.3     Shrunk   1.6      2.3        3.2    2.1     Clarity     Unshrunk 81       87         87     88     Shrunk   80       84         83     87     Gloss              87       84         87     88     Film Thickness (mils)     (related to MVTR data given below)     Unshrunk     Actual   0.96     0.80       0.77   0.75     MVTR 1     Unshrunk 0.60     0.67       0.60   0.55     Corrected              0.77     0.71       0.62   0.55     for 75 gauge     MVTR 2     Unshrunk 0.49     0.55       0.48   0.45     Corrected              0.63     0.59       0.49   0.45     for 75 gauge     ______________________________________

                  TABLE 10     ______________________________________            Example 7                   Example 8 Example 9                                      Example 10     ______________________________________     Modulus     LD       271,200  299,200   --     --     TD       292,100  337,900   --     --     Free Shrink     at 220° F.:     LD       --       --         13     13     TD       --       --         19     20     at 240° F.:     LD       20       17         20     18     TD       28       23         30     27     at 260° F.:     LD       --       --         27     28     TD       --       --         37     38     Haze     Unshrunk --       --        1.7    1.8     Clarity     Unshrunk --       --        82     84     Gloss              --       --        84     85     Film Thickness (mils)     (related to MVTR data given below)     Unshrunk 0.86     0.76      0.86   0.77     Shrunk   1.00     0.97      --     --     MVTR 1     Unshrunk 0.51     0.56      --     --     Shrunk   0.41     0.46      --     --     Corrected     for 75 gauge     Unshrunk 0.58     0.57      --     --     Shrunk   0.55     0.59      --     --     MVTR 2     Unshrunk 0.45     0.47      0.42   0.43     Shrunk   0.35     0.38      --     --     Corrected     for 75 gauge     Unshrunk 0.52     0.48      0.48   0.44     Shrunk   0.47     0.49      --     --     Tear (grams)     LD       --       --        8.6    5.0     TD       --       --        8.4    6.1     ______________________________________

                  TABLE 11     ______________________________________     Example 11    Example 12                             Example 13                                       Example 14     ______________________________________     Modulus     LD      345,750   352,880   322,950 320,470     TD      374,990   392,020   334,660 319,420     Free Shrink     at 240° F.:     LD      20        17        18      14     TD      29        23        24      25     Haze     Unshrunk             48.5      1.3       3.3     5.3     Clarity     Unshrunk             21        85        74      64     Gloss             107       89        73      64     Film Thickness (mils)     (related to MVTR data given below)     Unshrunk             0.85      0.81      1.40    1.60     MVTR 2     Unshrunk             0.36      0.36      0.23    0.19     Corrected for             0.41      0.39      0.43    0.41     75 Gauge     Tear (grams)     LD      --        --        8.6     5.0     TD      --        --        8.4     6.1     ______________________________________

                  TABLE 12     ______________________________________                  Example 19                          Example 20     ______________________________________     Modulus     LD             300,890   307,380     TD             315,460   291,480     Free Shrink/Shrink Tension     at 220° F.:     LD              8/440    14/395     TD             19/632    20/595     at 240° F.:     LD             18/477    21/439     TD             28/654    27/611     at 260° F.:     LD             28/446    29/436     TD             38/621    35/601     at 280° F.:     LD             44/467    43/487     TD             52/600    46/587     at 300° F.:     LD             59/--     60/--     TD             62/--     61/--     Haze     Unshrunk       1.6       1.8     Clarity     Unshrunk       76        76     Gloss                    89        86     Film Thickness (mils)     (related to MVTR data given below)     Unshrunk       1.09      1.12     MVTR 2     Non-shrunk     0.35      0.33     Corrected for  0.51      0.49     75 gauge     Tear     LD             6         6     TD             6         7     Tensile     LD             19,415    20,407     TD             19,296    16,990     Elongation     LD             63        62     TD             71        77     Ball Burst                    12        11     OTR                    3.0       4.5     ______________________________________

                  TABLE 13     ______________________________________             Example 17 Example 23                                  Example 24     ______________________________________     Modulus     LD        398,000      420,000   437,000     TD        442,000      473,000   488,000     Free Shrink     at 220° F.:     LD        15           14        15     TD        19           19        22     at 240° F.:     LD        20           19        19     TD        26           26        28     at 260° F.:     LD        30           30        26     TD        38           36        38     at 280° F.:     LD        44           44        44     TD        51           51        52     at 300° F.:     LD        64           63        62     TD        68           67        68     Haze     Unshrunk  1.8          2.0       1.2     Clarity     Unshrunk  82           81        81     Gloss               86           83        89     Film Thickness (mils)     (related to MVTR data given below)     Unshrunk  0.89         0.91      0.82     MVTR 2     Unshrunk  0.33         0.36      0.33     Corrected for               0.39         0.44      0.36     75 gauge     Tear     LD        1            7         4     TD        5            7         6     Tensile     LD        28,000       31,000    28,000     TD        29,000       33,000    29,000     Elongation     LD        80           86        84     TD        71           52        73     ______________________________________

In a typical working example of making the film of the present invention:

An ethylene propylene copolymer (Fina 8473) containing about 4% by weight ethylene, was blended with the polypropylene in a blend ratio of about 92% by weight EPC and 8% by weight PP. (The PP percentage includes the additives discussed above).

The EPC/PP blend was then blended with a hydrocarbon resin (Regalrez 1128 from Hercules) in a blend ratio of about 90% by weight EPC/PP and 10% by weight HC.

A second blend was also prepared, in a blend ratio of about 84.5% by weight PP (Exxon PD 4062 E7), 15% by weight HC (Regalrez 1128), and 0.5% white mineral oil (Kaydol from Witco Chemical).

A circular coextrusion die was fed with three extruders to prepare a five layer shrink film. One extruder was used to feed the blend of EPC or polypropylene, and HC, as a melt to the extrusion die to form the outer layers. Another extruder fed a polypropylene (Exxon PD 4062 E7) to the extrusion die to provide the intermediate layers in the multi-layer film. The third extruder provided the second blend of PP and HC to the extrusion die.

The extruded tape was rapidly cooled to room temperature and collapsed by pinch rolls. The tape was subsequently heated to an orientation temperature. Using a bubble technique well known in the art, internal air pressure stretched the tape to about 4.5 times its unstretched dimensions in the longitudinal (machine) direction and about 4.0 times its unstretched dimensions in the transverse direction to form a bubble which provided biaxial orientation to the resulting film. The bubble was then rapidly cooled by chilled air in order to maintain the oriented state of the film. Finally, the bubble was collapsed and the expanded film gathered on a take-up roll. After orientation, the total wall thickness of the film was about one mil with 50% of the structure being the blend of ethylene propylene copolymer and polypropylene; 15% of the structure being the intermediate layers; and the remainder or 35% of the structure being the core layer.

It will be clear to one skilled in the art that the degree of stretching may be varied to obtain the desired degree of film gauge or thickness and to regulate the desired amount of shrink tension, free shrink, and other shrink properties of the final film, depending on the packaging application. Preferred stretching or racking ratios are between about 3.0 and 8.0 in both the machine and transverse directions.

The multi-layer film of the present invention is preferably not irradiated. However, the sealant material, if extrusion laminated, extrusion coated, or conventionally laminated to the substrate moisture barrier film, can itself be irradiated or electronically or chemically crosslinked prior to lamination. Irradiation may be accomplished by means well known in the art.

The blend ratios of the EPC and PP may be varied according to desired properties or end-use of the multi-layer film. For example, increasing the polypropylene in the blend will add stiffness to the film, but also increase the sealing temperature of the film. Conversely, increasing the EPC in the blend tends to lower the shrink temperature of the oriented film, or to increase shrink at the same temperature, and also lowers the sealing temperature of the film. A preferred blend includes between about 4% and 15% PP and between about 96% and 85% EPC.

The multilayer film of the present invention is preferably oriented either monoaxially or biaxially, and preferably used as a shrink film. optionally, the oriented film may be further processed by reheating the film to a temperature near its orientation temperature, i.e. either somewhat below, at, or somewhat about its orientation temperature, to heat set the film. This future processing step has the advantage of substantially retaining many of the favorable physical characteristics of an oriented film, such as higher tensile strength, modulus and improved optical properties, while providing a substantial shrink-free film in applications where a shrink feature is undesirable.

The film of the present invention can utilize hydrocarbon resin in at least one or more, or even all the layers of the film, as long as the HC resin in any given layer is compatible from a process and performance point of view with the resin with which it is blended.

Films in accordance with this invention are preferably oriented, and preferably heat shrinkable. Preferred films exhibit a free shrink at 240° F. of at least 10% (LD) and 15% (TD), more preferably at least 15% (LD) and 22% (TD).

Obvious modifications to the invention as described may be made by one skilled in the art without departing from the spirit and scope of the claims as presented below. 

What is claimed is:
 1. A thermoplastic multi-layer film comprising:(a) a core layer comprising an oxygen barrier material; (b) two intermediate layers, on opposite surfaces of the core layer, comprising polyamide; (c) two tie layers, each disposed on a respective polyamide layer, comprising a polymeric material selected from the group consisting of:i) polymeric adhesive; ii) ethylene/alpha olefin copolymer; and iii) ethylene/vinyl acetate copolymer; d) two moisture barrier layers, adhered to respective tie layers, comprising blend of propylene polymer or copolymer, and a hydrocarbon resin; and e) two outermost layers comprising a polymeric material selected from the group consisting of:i) propylene polymer, ii) propylene copolymer, iii) ethylene/alpha olefin copolymer, and iv) polybutene.
 2. The film of claim 1 wherein the film is heat shrinkable. 